Autoimmune diseases, such as multiple sclerosis, rheumatoid arthritis, diabetes and lupus, etc., affect approximately 50 million Americans. The immune responses of self-reactive T lymphocytes play critical roles in autoimmune diseases. Therefore, identification of novel molecules that regulate T cell immune functions are important for a better understanding of the mechanisms underlying the disease development and for seeking novel therapies. During the current finding period, we have discovered that the type III histone deacetylase Sirt1 as a critical suppressor to T cell immunity and macrophage activation by suppressing the transcription factors AP-1, indicating Sirt1 as a potential therapeutic target for autoimmune and inflammatory diseases. In fact, we further demonstrated that the Sirt1 activator resveratrol prevents/treats type 1 diabetes in mice. Our preliminary study of the current competitive renewal application demonstrates that the deacetylase Sirt1 and the acetyltransferase GCN5 oppositely regulate T cell activation. Genetic deletion of GCN5 gene inhibits T cell immune responses in mice, identifying GCN5 as a critical positive regulator for T cell immunity. Interestingly, treatment of mice with GCN5 specific inhibitor attenuated autoimmune disease development. Therefore, based on the above preliminary findings, we propose that the histone deacetylase Sirt1 is a negative regulator and the acetyltransferase GCN5 is a positive regulator for T cell immunity, and that the Sirt1 activator and GCN5 inhibitor have great therapeutic potentials in treatment of autoimmune diseases. This project is to address this hypothesis using the state-of-art approaches of both immunological and molecular studies. Results from this proposed study discover novel molecular mechanisms behind Sirt1 and GCN5 in T cell activation and autoimmunity, providing rationales for the uses of Sirt1 deacetylase activators and GCN5 acetyltransferase inhibitors in treating/preventing autoimmune diseases.